The present invention relates generally to the field of mobile phones and deals more particularly with imaging capable mobile terminals and systems.
A mobile communication terminal equipped with an electronic camera is a multipurpose device for capturing, transmitting and receiving still images, video and audio, and other possible forms of communication. The wide variety of possible uses and applications imposes a limiting and contradictory demand to the optical and mechanical properties of the camera. For example, when such a mobile communication terminal is used as a personal video telephone, the camera is expected to be on the same side of the terminal as the display so that the user can see the display while the camera is pointing at him/her. On the other hand, in a photography application, it is desirable and beneficial for the user to see the display while the camera is pointing in the same direction that the user is looking at. This contradiction in demands is partially solved by a swivel mechanism that allows the camera to rotate towards and away from the user as described, for example, in U.S. Pat. No. 5,612,732 issued Mar. 18, 1997 entitled xe2x80x9cPortable Compact Imaging and Displaying Apparatus with Rotatable Camera.xe2x80x9d A rotatable camera head may also be necessary to accommodate a lens barrel that long compared to its diameter to provide a compact carrying position wherein the barrel folds into the body of the device case.
In some instances, a macro or close-up lens, is desired to enable imaging and image capture from very short object distances for example within a few millimeters. An example of such an application is the use of the camera as a scanner for capturing text, handwriting, numbers, bar codes or other applicable information. These types of applications call for short object distances and if the object distance is relatively long, for example, 20 to 30 centimeters, the object is rendered very small on the focal plane making further processing such as object separation and recognition much more difficult as the spatial resolution is decreased and the desired object is further surrounded by unwanted objects. If the magnification of the optical system is increased, the angle or view of the camera becomes very small making it extremely difficult to hold the camera accurately positioned and aimed at the object image to be captured.
One possible solution to accommodate close-up and non close-up imaging requirements is to provide a camera with a swiveled close-up lens. However, the requirement of an additional close-up lens may result in a fragile or unnecessarily complex mechanical structure because the mechanism for turning the close-up lens in front of the main lens assembly must move or rotate together with the camera to accommodate the requirements of the different orientations of the communication terminal as described above.
Applicants are not aware of the existence of mobile phones with close-up shooting capable cameras. Some personal digital assistant (PDA) devices, for example, Sharp Zaurus, feature a close-up imaging mode. However, the shortest object distance is still relatively long, about 10 to 15 centimeters. In the case of PDA devices, the close-up mode is implemented by ordinary zoom optics and not with an external close-up lens. A similar structure, i.e., zoom optics, is used in some conventional cameras and digital still cameras, however, such implementation does not allow object distances short enough for optical character recognition (OCR) use with the difference between a close-up imaging mode and an OCR imaging mode being about a ten-fold difference.
Separate close-up lenses can be found in system cameras, broadcast television cameras, and so forth as an add-on accessory. These accessory close-up lenses typically enable very short object distances compared to the focal lens of the main optics, but a detachable close-up lens is not a viable option in mobile phones.
It is an object therefore of the present invention to provide an economical implementation of a close-up imaging capability in a mobile phone equipped with a camera.
It is a further object of the present invention to provide a close-up lens in a mobile phone for text recognition by means of optical character recognition (OCR) techniques.
It is a further object of the present invention to provide a mobile phone with a close-up lens for photographing very small objects to enhance the versatility of the mobile phone.
According to a broad aspect of the present invention, an imaging capable mobile terminal comprises an imaging lens arrangement having a first focal length in one direction and a second focal length in another direction wherein the second focal length is shorter than the first focal length with the aid of an optical component which shortens the focal length of the lens arrangement.
According to a further aspect of the imaging capable mobile terminal of the present invention, the optical component of the lens arrangement comprises a close-up lens.
In another aspect of the imaging capable mobile terminal of the present invention, the optical component of the lens arrangement comprises a close-up lens and a reflector for folding the optical path length of the lens arrangement.
In a yet further aspect of the imaging capable mobile terminal of the present invention, the optical component of the lens arrangement comprises a concave reflector placed in front of the lens arrangement to intercept the optical path length of the lens arrangement.
In a still further aspect of the imaging capable mobile terminal of the present invention, the imaging lens arrangement further comprises a camera lens wherein one of the camera lenses or the optical component is held in a fixed position and the other camera lens or optical component is arranged for movement relative to one another to shorten the focal length of the lens arrangement.
In accordance with another aspect of the present invention, a lens system capable of close-up imaging for use in a mobile terminal comprises in order from an object side, an optical component which shortens the focal length, an imaging lens arrangement wherein the optical component is fixedly held in a wall portion of the mobile terminal, and a main camera lens carried by a rotatable camera assembly whereby the camera assembly is rotated into position behind the optical component for close-up imaging.
In accordance with a further aspect of the present invention, a method for close-up imaging in an imaging capable mobile terminal comprises the steps of providing an imaging lens arrangement having a first focal length in one direction and a second focal length in another direction, providing an optical component, and shortening the focal length of the lens arrangement with the aid of the optical component whereby the second focal length is shorter than the first focal length for close-up imaging.